The present invention relates to a method for building an underground structure of a building, and more particularly, to a method for building an underground structure which is capable of utilizing a retaining wall installed temporarily as a part of a permanent structure of a building, thereby economically constructing a retaining wall of the underground structure, and also utilizing structure members used in a main construction, without any installation of temporary struts for earth construction.
So as to utilize a limited land effectively, generally, the depth of excavating into the underground in the downtown areas becomes deeper. Upon the underground excavating, an retaining wall is necessarily installed to protect existing facilities such as adjacent buildings, roads, etc. Even though a high construction cost is consumed for the installation of the retaining wall, it has been designed and constructed, while being considered as temporary construction facilities. The retaining wall exhibits a function of enduring an earth pressure, water pressure, upper member load and the like, until the building structure is completed. Then, if the building structure has been completed, the retaining wall is buried or in some cases of certain construction sites, disassembled and removed, thereby being treated as a separate structure from an underground retaining wall structure of the building. Even though the retaining wall has the same function as the underground retaining wall of the building, the retaining wall and the underground retaining wall are individually designed and constructed, which causes the unnecessary consumption of the construction cost. In addition, since it is necessary to design and construct the retaining wall at the minimum cost, there may occur a problem that a safety is relatively reduced, such that the retaining wall may be broken against an unexpected load.
There are several kinds of temporary retaining walls which are used for building a site for the structure under the ground. For example, a method for driving in an H-section steel pile into the ground and inserting an earth plate between the H-section steel piles, a soil cement wall (SCW) construction method, a cast-in-place concrete pile (CIP) construction method and a soil nailing wall construction method are commonly used. These methods generally form a wall body in the underground to bear against an external force such as an earth pressure, a water pressure and the like, and support the wall body by means of a strut installed in the interior of the wall body, pull the wall body by means of an earth anchor, or punch the original ground to reinforce the wall body with a soil nail. According to the axial force of the strut or earth anchor it will generate a fatigue of the material, which may cause a structural defect. As a result, the strut or earth anchor is considered as temporary structure. On the other hand, though the H-section steel pile, SCW, CIP and soil nailing wall which are driven in into the ground can be assembled with the outside retaining wall of the building to be thereby recycled as a part of the permanent structure, they are buried in the ground.
When the retaining wall is installed as the temporary facilities, an retaining wall line should move back towards the outside to occupy the working space required, since the working space for building the underground retaining wall is further needed. Therefore, an excavated amount increases as much as the movement of the retaining wall line, with a consequence that an amount of earth for filling the excavated site increases accordingly. In case of the soil nailing, the earth around the soil nailing processed portion theoretically exhibits an improved shear strength and is substantially independent. However, there is a problem that despite that the earth pressure around the soil nailing processed portion is not applied on the structure, the retaining wall is still designed with the assumption that the earth pressure is applied on the structure.
The present inventor has made various studies to solve the above problems encountered in the conventional temporary retaining construction method and as a result, proposes a novel underground retaining wall building method for permanently utilizing the temporary retaining wall which is disassembled or buried after a predetermined time elapses in the previous art, as a part of the retaining wall of the underground structure.
For the purpose of installing a structure in the ground, a general building method which comprise installing the temporary retaining wall, supporting the wall against the load by means of struts, and building the structure in order from the base in the ground to the upper portion thereof has been adopted. At this time, as the struts are temporary facilities, they only work as obstacles to the structure construction. In more detail, due to the struts, it is very inconvenient to unload construction materials or cast the concrete, or there is an inconvenience that the struts should be removed or reinstalled at another place during the construction. If it is possible to utilize a steel strut as a part of the permanent structure, the work for disassembling and removing the steel strut is not required, which makes the working processes of the structure more simple.
The present inventor has also studied a method of using a beam or girder installed in a permanent structure as a strut for a temporary construction.
Accordingly, an object of the present invention is to provide a method for building an underground structure which is capable of utilizing an retaining wall installed temporarily for excavating a site for the underground structure of a building as a part of a permanent structure. Another object of the present invention is to provide a method for designing a structure which is capable of utilizing an retaining wall installed temporarily for excavating a site for an underground structure of a building as a part of a permanent structure.
Yet another object of the present invention is to provide a method for building an underground structure which is capable of preventing the underground structure from floating.
Still another object of the present invention is to provide a method for building an underground structure which is capable of utilizing a strut installed temporarily for excavating a site for the underground structure of a building as a part of a permanent structure.
According to the first aspect of the present invention, there is provided a method for building an underground composite retaining wall, which includes the steps of: determining a position where a temporary retaining wall is installed in the consideration of the outside line of the underground of a building, forming holes by means of a construction equipment such as an auger drill to drive in an H-section steel pile into each of the holes, and installing an earth plate between the H-section steel piles, thereby completing the installation of the temporary retaining wall; excavating a site in the interior of the temporary retaining wall; if the excavation of the construction site is completed, installing a anchored shear connecting means on the H-section steel pile; arranging reinforcing bars on an underground retaining wall; and installing form in the inside of the underground retaining wall, casting concrete in the form and curing the concrete, thereby completing the formation of the underground retaining wall.
According to the second aspect of the present invention, there is provided a method for building an underground structure by utilizing a part of a permanent structure as a strut for earth work, which includes the steps of: driving in an H-section steel on a boundary line at which a building is constructed; driving in a center pile on a position where the pillar of the building is installed; carrying out a primary earth excavating work; coupling the H-section steel pile with a concrete retaining wall by means of a anchored shear connecting means, thereby constructing an underground composite retaining wall; installing a girder to be used as a part of a permanent structure on the composite retaining wall by means of an embedded plate and assembling and disposing the girder to the center pile; and carrying out a secondary earth excavating work and repeating the steps after the primary earth excavating work until the earth is excavated up to the lowermost portion of the building.